Variable-speed transmission



March 1952 H. M. STEPHENSON VARIABLE-SPEED TRANSMISSION Filed Jan. 17, 1950 gig 22 /6 3/ v Inventor:

,l-lugh M. StephenS y B-hs Attorney Patented Mar. 25, 1952 VARIABLE-SPEED TRANSMISSION f Hugh M. Stephenson, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application January 17, 1950, Serial No. 138,993

1 Claim. 1

This invention relates to variable speed devices of the type wherein power is transmitted at desired ratios by a plurality of caged balls rolling under pressure between two or more races of variable peripheries.

Devices of this type are well-known and it is the principal object of this invention to provide a new and improved form of such a device wherein speed changes may be smoothly, continuously and conveniently made over a relatively wide speed range. In one form of the invention the transmission speed ratio is automatically adjust-' 3 and 4 show the operating positions of certain elements of Fig. 1 for various speed transmission ratios. I

Referring now to Fig. 1, there is shown a variable speed transmission having an input shaft and an output shaft 2. The transmission is generally symmetrical. about longitudinal axis and accordingly only the portion of the transmission above axis 5 is shown in Fig. '1. Shaft 1| is intended to be the extension of a shaft of a source of driving power such as a motor (not shown) and accordingly shaft is suitably supported by bearings (not shown) which are external to the variable speed transmission. Output shaft 2 is adapted to drive a load device (not shown). The general function of the variable speed transmission which is interposed between shafts and 2 is to vary the speed ratio therebetween.

Shaft I is provided with an externally splined portion 3 which carries a pair of driving races 4 internally splined to mate with spline 3. The transmission is further generally symmetrical, with the exception of constructional details of input shaft and output shaft 2, about a plane 6 normal to axis5 and appearing as a vertical center-line 6 in Fig. 1. Driving races 4 which are oppositely positioned with respect to plane 6 are slidable with respect ,to splined portion 3 of shaft and tend to be forced apart by a plurality of helical compression springs 1. By this construction, the pressure on the driving races 4 is identical and no end thrust is placed o th i ng sha t.

A pair of driven cages 8 and 8 are solidly linked together by a torque tube 9 and the assembled combination is supported on a pair of bearings |0 positioned in a pair of end flanges II which form a portion of the casing of the transmission. Output shaft 2 is secured to cage 8' by the use of a key l2 so that shaft 2 rotates with the assembly of cages 8 and 8 and tube 9. The ends of tube 9 are slotted-to form a plurality of equally spaced projections l4 defined by walls 33. The slots between adjacent projection l4 provide cavities to accommodate the driving balls 32. The projections l4 are positioned in slots 8| formed in cages 8 and 8. The outer peripheral surfaces of projections I4 are threaded and the assembly is secured by nuts I3.

End flanges are connected together by an outer casing l6 having a generally cylindrical inner surface l1. Surface I! is maintained in a concentric relationship with axis 5 by a pair of rabbets l8 forming part of end flanges The assembly of end flanges II and casing I8 is suitably clamped together by a plurality of studs l9 and nuts 20. A pair of oil seals l5 are positioned in end flanges II to prevent outward leakage of oil around shafts I and 2.

A pair of outer or control races 2| are supported on inner surface I! of easing l6. Races 2| are free to move axially along inner surface I! but are restrained from rotational movement by a plurality of studs 22 threadedly engaged in casing l6 and arranged for sliding engagement with a plurality of axial slots 23 in the outer peripheries of races 2|. As in the case of races 4, races 2| are oppositely positioned with respect to plane 6. An intermediate adjuster ring 2 4 is supported on the inner surface I! of casing 6 and is positioned symmetrically between races 2|. Adjuster ring 24 is rotatable about axis 5 and is employed in the adjustment of the speed ratio of the transmission as will be more fully described hereinafter. Rotation of ring 24 is effected by an adjusting screw 25 threadedly engaged with a hobbed portion 26 on the periphery of ring 24. Screw 25 is journaled in a block 21 suitably fixed to casing l6. Screw 25 may be rotated by any suitable external turning device (not shown), such as a crank.

' Attention is now directed to Fig. 2 which is a view of certain of the elements of the variable speed transmission without outer casing I6. In

particular, adjuster ring 24 including hobbed portion 26 thereof, outer races 2| and driven cages 8 and 8 are shown in the same relative positions as in Fig. 1. In the spaces between ring 24 and ,outer races 2| are provided two assemblies of adjuster balls each assembly comprising a plurality of balls 28 equally spaced by a cage 29. Adjuster ring 24 and races 2| are provided with a plurality of mating cam surfaces 3|! and 30', respectively, which are most clearly shown in Fig. 2 and with which adjuster balls 28 are arranged to engage. Cam surfaces 30 and 30 may be conveniently formed by milling. Since rotation of outer races 2| is prohibited by the engagement of studs 22 with axial slots 23 formed in the outer periphery of the races 2|, the rotation of adjuster ring 24 causes the distance between races 2| to be varied. The manner in which this adjusting action effects the operation of the variable speed transmission will be more fully explained hereinafter.

Driven cages 8 and 8' are provided with a plurality of sockets 3|, defined by concave surfaces, which may be conveniently termed spin sockets, and in each of these sockets is positioned a driving ball 32. As will be seen in Fig. 1, driving balls 32 contact simultaneously sockets 3| of driving cages 8 and 8'- and race surfaces 4' and 2 respectively of races 4 and 2 Sockets 3| are preferably symmetrically spaced about the axis of cages 8 and 8'. For convenience the two sets of driving balls 32 in the transmission may be angularly offset with respect to each other and thus in Fig. 1 there is shown a ball 32 at the right of plane 6 which lies in the plane of the sectional view shown in Fig. 1, while the ball at the left of plane 6 lies behind the plane of the sectional view shown in Fig. l.

Rotation of driving shaft by the source of driving power causes rotation of driving races 4 which are free to slide on spline 3 and are forced in contact with balls 32 by springs 1. Balls 32 are further forced in contact with spin sockets 3! and outer races 2!, the exact position of balls 32 depending on the axial position of races 2| with respect to the vertical center line 6. While the surfaces 4' and 2| of races 4 and 2| respectively, which engage balls 32, may be provided with various annular curvatures, a convenient surface to employ is a simple conical surface as shown in Fig. 1. r I

As previously mentioned the position of races 2| is adjustable by action of adjuster 24 and adjuster balls 28. Rotation of screw 25 by external means causes corresponding rotation of adjuster 24 on surface By rotating adjuster 24, balls 28 may be caused to occupy various positions on cam surfaces 30 and 30', causing races 2| to be moved inwardly or outwardly with respect to plane 3 depending on the direction of rotation of adjuster 24. Such variation in the position of races 2| varies the radius of the circle described by the rotation of the balls 32 about axis 5.

In Fig. 1 races 2| are positioned in their maximum outward position with respect to plane 6 and in this condition the transmission is adjusted for a theoretical infinite ratio or in other words, the driven cages are not rotated by action of driving balls 32 and the speed of output shaft 2 is zero. In practical cases it may not be convenient to obtain such a ratio due to excessive pressures in the driving balls and races, but this condition is shown by way of example since it represents an extreme position of driving balls 32 with respect to spin sockets 3| and races 4 and 2|.

Since balls 32 are generally similar, operation of the transmission may be described in terms of a single ball. As race 4 rotates, contact is made with ball 32 at a roll point 34 causing the ball to roll on surface 4' and rotation of ball 32 is efiected about a spin axis 35 passing through the center of ball 32 and contact point 31 of spin socket 3|. The speed of rotation of ball 32 is determined by the radius thereof and the radius of driving race 4 at point 34. It will be noted that since ball 32 is physically confined in spin socket 3| by reason of the compression of springs I which resist the tendency of the balls 32 to roll out of the concave socket 3| and thereby prevent contact between the balls 32 and the walls 33 of the projections |4, rolling action of ball 32 relative to driven cage 8' may not occur. It is a basic characteristic of this device that the spin axis of the balls 32 always pass through the center of the balls 32 and their point of contact with the concave socket 3 Under the conditions shown in Fig. 1; ball 32 rolls relative to driving race 4, but spinning engagement is effected thereby with intermediate race 2| and spin socket 3|. There is no tendency, therefore, for cage 8' and shaft 2 .to be driven by ball 32 and driven cage 8'v is effectively locked to the restrained outer race 2 Referring now to Fig. 3, ball 32 is shown at the mid-position of its adjustment. More particularly, the spacing of control race 2| and adjuster 24 is diminished by rotation of adjuster 24 and the repositioning of adjuster balls 28 in mating cam surfaces 30 and 30'. Thus, the point of contact 36 of ball 32 with race surface 2| is moved radially outward from shaft 5. Ball 32 contacts spin socket 3| at point 31' which in the arrangement of Fig. 3 is the mid-point of socket 3|. Driving race 4 is maintained in contact with ball 32 at point 34' by springs I and therefore as driving race 4 is rotated, ball 32 is caused to roll relative to race 4 at point 34' and race 2| at point 36. Rotation of ball 32 occurs about a spin axis 35 passing through the center of ball 32 and contact point 31'. Again ball 32 is in spinning engagement with socket 3| and rolling engagement with driving race 4, but it will be noted that there is rolling engagement between ball 32 and race 2| rather than spinning contact as in the case of Fig. 1. Spin axis 35' is now parallel with main axis 5.

The rotational speed of ball 32 about spin axis 35' is determined by the radius of driving race 4 at point 34 and the effective radius of ball 32 from point 34 to spin axis 35'. Balls 32 are further caused to rotate in their respective groups about main axis 5, in the well-known manner of planetary gearin and since balls 32 are restrained by sockets 3|, driven cages 8 and 8' are caused to follow the balls 32 revolving around main axis 5. Under the condition shown in Fig. 3, driven cages 8 and 8' rotate at a lower speed than driving races 4 or, in other words, a speed reduction is effected in the transmission between the driving races and driven cages and, accordingly, between the input and output shafts. By rotating adjuster 24 so that the balls 32 assume positions intermediate those illustrated in Figs. 1 and 3, it is apparent that intermediate speed reduction ratios can be affected.

Referring now to Fig. 4, control race 2| is shown adjusted to its maximum inward position with respect to adjuster 24. This adjustment is effected by further rotating adjuster 24 to permit adjuster balls 28 to contact the deepest portion of mating cam surfaces 30 and 30. In Fig. 4 the conditions shown in Fig. 1 are in one sense reversed in that ball 32 now spins at an extreme outward point 3'!" in socket 3|. Ball 32 contacts control race 2| at point 36" and driving race 4 at point 34". While there is a tendency for driving race 4 to cause ball 32 to roll about an axis intersecting the center of ball 32 and point 36" on race 2|, such rotation requires rolling action of ball 32 relative to driven cage 8. Since ball 32 is confined in socket 3| and is limited at all times to spinning action relative to cage 8', rotary motion of driving race 4 causes rolling action of ball 32 relative to control race 2| at point 36". Such rolling action causes rotation of ball 32 about a spin axis 35" between points 34" and 3?" on race 4 and socket 3|, respectively. Under this condition driving race 4 is effectively locked to spin socket 3| and therefore driven cage 8' rotates with driving race 4 at the driving speed thereof. The speed transmission ratio is, therefore, one-to-one, or in other words a straight-through drive is provided.

It will thus be seen that the invention provides a variable speed transmission havin a speed range varying from one-to-one to a theoretical value of infinity with a constant speed input. While, as previously noted, such a speed range may be impractical, nevertheless, a relatively wide range may be obtained which is adequate for most practical applications. The variation in speed transmission ratio is obtained in the device shown by positioning control races 2| at various positions relative to spin sockets 3|, thereby causing driving balls 32 to contact spin sockets 3| and driving race 2| at various points. A particularly convenient mechanism is provided for positioning races 2| by the use of adjuster ring 24 and adjuster balls 28 moving in mating cam surfaces 30 and 30 in adjuster 24 and races 2|. While an adjusting screw 25 and a mating hobbed portion 26 of adjuster 24 are shown as a means of rotating adjuster 24 and cams 3|! thereof relative to races 2| and cams thereof, it will be obvious that other well-known devices may be employed to secure such relative motion. Furthermore, configurations of cam surfaces other than those shown herein may readily be employed in combination with other arrangements of adjuster balls.

It will be understood that in the device shown in Fig. 1 all thrust forces are contained within the transmission through the use of oppositely disposed driven cages 8 and 8' interconnected by torque tube 9. In other words, the transmission is in effect double-ended. It will be obvious that by providing suitable thrust bearings the device may readily be made single-ended or, in other words, the combination of single driving and control races and a single driven cage may be employed with corresponding single groups of driving balls and adjuster balls and associated cam surfaces.

In the arrangement described control races 2| are restrained from rotation relative to inner surface I! by the use of studs 22 in slots 23 of races 2|. There is, however, under most conditions a reaction in races 2| from rotary motion of balls 32. This reaction tends to cause rotation of races 2| in a direction opposite to the rotation of driving races 4, due to planetary differential action through balls 32. Any rotational motion of races 2| tends to cause motion of cam surfaces 30' relative to adjuster balls 28 and cam surfaces 30 in adjuster 24. Relative motion of cams 3|! and 30 tends to cause outward axial motion of races 2|, thereby tending automatically to increases the driving ratio between driving race 4 and driven cases 8 and 8' in proportion to the torque demanded by the driven or output shaft. Thus, by the simple modification of removing restraining studs 22 and permitting free floating of races 2|, the transmission is made automatically torque-responsive so that with a constant input speed and variable torque demand the transmission instantly responds to furnish proper ratio and torque to supply a driven load within practical ratio limits of the transmission.

While I have shown and described a preferred embodiment of my invention, it will be understood that my invention may well take other forms and I, therefore, aim in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

In a power transmission device in combination a pair of oppositely disposed rotary driving races, a pair of oppositely disposed interconnected rotary driven members each having a plurality of spin sockets therein, a pair of oppositely disposed control race members each having a race and a plurality of cam surfaces therein, a plurality of driving balls arranged in distinct groups each associated with one of said driven members, said balls engaging said control races and being in spinning contact with said sockets, means to maintain said driving races in engagement with said balls, means to vary the positions of said control races relative to said sockets comprising an adjuster member interposed between said control race members and having a plurality of cam surfaces therein arranged to mate with said first-mentioned cam surfaces in said race members, a plurality of adjuster balls arranged to engage said mating cam surfaces, means to move said last-mentioned cam surfaces relative to said first-mentioned cam surfaces to vary the spacing between said adjuster and said control races, variation in the points of spinning contact of said driving balls in said sockets being effected by relative motion between said mating cam surfaces in engagement with said adjuster balls, and the speed ratio between said driving race and said driven member being varied in response to said last-mentioned variation.

HUGH M. STEPHENSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,380,006 Nielsen May 31, 1921 1,585,140 Erban May 18, 1926 1,691,625 Chilton Nov. 13, 1928 1,718,846 Arter June 25, 1929 1,800,388 Jacobsen Apr. 14, 1931 2,005,949 Morgan June 25, 1935 2,349,981 Mulder May 30, 1944 FOREIGN PATENTS Number Country Date 474,289 Great Britain Oct. 25, 1937 

